fix(deps): update dependency com.google.api:gapic-generator-java-bom to v2.15.3 (#9217)

Author: renovate-bot

java-shared-dependencies/first-party-dependencies/pom.xml

@@ -21,7 +21,7 @@
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <site.installationModule>${project.artifactId}</site.installationModule>
-    <gapic-generator-java-bom.version>2.15.2</gapic-generator-java-bom.version>
+    <gapic-generator-java-bom.version>2.15.3</gapic-generator-java-bom.version>
     <grpc-gcp.version>1.4.1</grpc-gcp.version>
     <gson.version>2.10.1</gson.version>
     <google.http-client.version>1.43.1</google.http-client.version>